Reduced Size Spiral Antenna

The cavity backed spiral antenna with a square configuration is described. It is shown that with continual development and an invention of a unique design of cavity the aperture of this type of antenna is reduced to approximately 0.1λ square at its lowest operating frequency. The antenna radiates circularly polarised energy with a uni-directional beam over a decade frequency band. It is shown that the match of the antenna is better than 2:1 over the entire frequency band and that its gain is relatively high when its aperture dimensions are taken into consideration.